Polyurethane tissue adhesives for annulus fibrosus repair: Mechanical restoration and cytotoxicity

The microdiscectomy used for the treatment of intervertebral disc disorders leaves an open incision in the annulus fibrosus that must be sealed to avoid re-herniation and other subsequent degenerations. In this study, we developed an injectable and in situ polymerizable polyurethane adhesive as a long-term post-surgical annulus fibrosus repair strategy. It was investigated the chemical structure of the urethane-based adhesive and its physico-chemical, viscoelastic, kinetic, and in vitro cytotoxic properties. The adhesive formulated from the polycarbonate diol with the highest molar mass was the one that exhibited a compressive behavior closest to the intervertebral disc outer region, and therefore, the most suitable for restoration. This adhesive showed 18-day stability under moisture and required a preparation time of 10 h at 60°C before use. The material also adhered covalently to gelatin (without catalyst or initiator) and positively impacted cell proliferation after its polymerization, which are essential requirements for clinical translation. These findings confirmed the ability of the polyurethane adhesive to act as an annulus fibrosus sealant, although further improvements in its formulation are necessary.